(1) Field of the Invention
The present invention relates to a dispersion of fine particles of modified polyethylene in an organic liquid and a process for the preparation thereof. More particularly, the present invention relates to a dispersion of fine particles of modified polyethylene, which is valuable as an additive of an oily printing ink, and a process for the preparation thereof.
(2) Description of the Prior Art
For improving the tack and abrasion resistance in an oily printing ink, especially a planographic or offset printing ink, polyethylene wax or the like is often incorporated in the printing ink. It is indispensable that the wax used for this purpose should be homogeneously incorporated in the ink.
As means for incorporating the wax in the ink, there are now adopted a method in which a pulverized wax is used, a method in which an unpulverized solid wax is kneaded, and a method in which a wax crystallized in an oil is used.
Of these printing ink waxes, the pulverized wax or unpulverized wax is defective in that since the wax particle size distribution in the ink is broad, if the wax is added in an amount sufficient to impart an abrasion resistance to the ink, the gloss of the printed image tends to decrease. The crystallized wax is defective in that since the wax is solidified if the wax concentration is increased, it is difficult to obtain an ink having a high wax concentration. As a compounding agent for a polyethylene wax for use in an oily printing ink, an aqueous emulsified dispersion or an aqueous suspended dispersion is prepared. Water is separated from it, and the reminder is used as a polyethylene wax compounding agent. Or an organic solvent is added to these solid particles, and the resulting product may be used as a compounding agent. To use these compounding agents for an oily printing ink, the water content of these compounding agents must be made as small as possible.
When products having a large water content are used as the compounding agents, troubles such as phase separation are liable to occur at the time of compounding, and these troubles impede the operation of manufacturing the oily ink production. At the same time, the operability will be markedly lowered. In order to remove water sufficiently from the aqueous emulfied or suspended dispersion, it is possible to perform such means as distillation under reduced pressure and dehydration by molecular sieves. These means cost very high or may involve inconveniences such as poor yields.